1. Field of the Invention
This invention relates to electronically-steerable antenna arrays for use in high frequency bands, such as SHF (3 gigahertz (GHz) to 30 GHz) and EHF (31 GHz to 300 GHz). The beam of such an antenna array is steerable by varying the phase gradient, or more broadly, the time gradient, across the array. More particularly, the invention relates to the use of lasers and other photonic components to perform the steering functions in the phased array.
2. Background Information and Description of the Prior Art
Antenna arrays are composed of a number of radiating elements suitably spaced with respect to one another. The beam of such an array can be steered in space by properly varying the phase gradient across the array, i.e. by varying the relative phases of the signals applied to the respective antenna elements. A number of devices are known which can provide the variable phase gradients.
More specifically, variable phase shifters can be used to obtain the desired phase (gradient across an array. In such an array, typically one phase shifter is needed per antenna element. Alternatively, a set of fixed phase shifters can be used, with associated switching components which provide for switching of the signal of a selected phase to each antenna element.
Antenna arrays are often used in applications such as aircraft and satellites. In these applications, space and weight constraints are, of course, highly significant. In addition, there is not a great deal of flexibility as to the location of component parts in such applications. Moreover, when EHF frequencies are involved, the space between antenna elements may be as small as 1/8 inch or less. This places further restrictions on the numbers and types of components that can be placed physically proximate to the elements themselves.
Variable phase shifters are not particularly useful in these applications because they can be bulky and complex. Further, variable phase shifters are not readily available at EHF frequencies. Similarly, fixed phase shifters can also be bulky, but more importantly, the switching matrix needed with fixed phase shifters can be large and complex.
One solution would be to locate the variable phase shifters, or the switching matrix if fixed phase shifters are used, at a position remote from the array. However, such a design would require a separate transmission line to be run from each antenna element to a variable phase shifter or switching circuit. Cutting and routing each line involves a cumbersome and labor intensive manufacturing step. Thus, the above-described solutions do not appear to be effective.
There remains a need, therefore, for a phased array for use in the microwave frequency bands, such as SHF and EHF, which conforms to the available space requirements in aircraft, satellites and other such environments and which array is relatively light-weight, low-cost and uses readily available components. Furthermore, there remains a need for such an array in which the phase shifters and switching components do not have to be physically proximate to the array elements.